Final answer:
The observed improvement in muscle function upon opening the eyes after fatigue suggests that fatigue is connected to the CNS. This is because the CNS is integral in generating action potentials necessary for muscle contraction.
Step-by-step explanation:
When a subject, with eyes closed, repeatedly contracts a muscle until fatigue occurs, and then sees an improvement in muscle function upon opening their eyes, this is a demonstration of fatigue being linked to the central nervous system (CNS). The CNS plays a crucial role in muscle contraction, as it is responsible for sending action potentials to the muscle fibers, which, in turn, produce work. This phenomenon illustrates how CNS input can modulate muscle force production – increasing the frequency of action potentials and the number of motor neurons transmitting these impulses can enhance the tension created in the muscles. In contrast, peripheral factors such as ATP depletion, lactic acid buildup, electrolyte imbalances, and structural damage to sarcomeres primarily affect the muscle at a local level.